Some projection-type image display devices (which is referred to as “projector” below in some cases) which project images onto a screen or others have been put to practical use, each of the projection-type image display devices having an interactive function that allows a user to efficiently and effectively make a presentation. In this manner, the user draws letters, figures, etc., on a display screen or performs a switching operation of a displayed image by performing an operation of drawing, etc., on the display screen projected onto a screen by using a finger, a dedicated pen (which is, more precisely, a “pen-shaped pointing tool” but simply referred to as “pen” in some cases) and etc.
Various methods of detecting a position of the pen or others relative to the display screen are proposed. For example, there are a method of identifying the position by detecting reflected light from the pen or others after emission of laser light, etc., onto the screen or by detecting a light-blocked state, a method of detecting a position at which laser light, etc., is emitted onto the screen, and other methods.
When the user utilizes such an interactive function, the user desires to, for example, switch attributions such as color and thickness of a drawn line or figure at any time. Conventionally, when the switching is performed by using a single pen, a switching method has been adopted, the switching method using a pallet achieved on a software basis and projected on the screen and selecting a region indicating an attribute such as desired color and line thickness by using the pen. On the other hand, a method is also proposed, the method preparing a plurality of pens and separately using the pens to which the different attributes such as color and line thickness are assigned, respectively.
For example, Japanese Patent Application Laid-open Publication No. 2012-221115 (Patent Document 1) describes a technique of detecting input of coordinates by using a plurality of pointing tools. In this technique, the plurality of pointing tools store unique identification information for distinguishing them from each other, and create a transmission signal including identification information and switch information indicating states of a plurality of switching means at a repetition cycle that is set uniquely to the identification information. A coordinates input device receives the transmission signals from the pointing tools, identifies the repetition cycle of the transmission signal for the pointing tool corresponding to the identification information detected from the received signal based on the identification signal, and generates transmission-signal timing information synchronizing with the repetition cycle.